The invention relates to position sensitive detectors, and more particularly, to one-dimensional optical position sensitive detectors.
One-dimensional position sensitive detectors have a wide range of applications in current electronics. They convert the position of an object of interest into an electrical signal that can be integrated into the electronic device, allowing for applications that require the monitoring of single-axis mechanical motion.
A linear (or “sliding”) potentiometer is often used as a position sensor. In the linear potentiometer, a resistive strip distributes applied potential. A metallic “wiper” contact moves along the resistive element. Potential on the wiper is determined by the position of the wiper contact along the resistive strip. However, constant wear and tear from frequent motion of the slider deteriorates the material over time which may eventually cause sensor failure. For this reason, a non-contact sensor is desirable for many applications.
Optical position sensitive detectors provide a non-contact method of tracking the location of a light spot [1]. Silicon-based versions of such sensors may be fabricated with standard CMOS technology, are inexpensive and provide a real-time, analog signal output corresponding to the position of the light spot.
There are two main classes of optical position sensors, or position sensitive detectors (PSDs). The first type is composed of discrete photo sensor elements that provide position information in the form of a digital output (e.g. CCDs [2] or linear array of discrete photodiodes). The second type is a sensor with a continuous photosensitive surface that provides position data in the form of an analog output (e.g. Lateral effect PSD [3][4][5]).
Lateral effect position sensitive detectors (LEPSDs) may be fabricated using standard CMOS processing techniques[6], and provide an analog output and a relatively low cost, accurate method of sensing position. However, LEPSDs require a backside contact which results in increased packaging costs. If a sensor could have all contacts on one side of the substrate, then the cost of the sensors and their packaging could be reduced by eliminating all backside processing and associated costs. Further, minimization of required readout circuitry is desired. Analog output position sensitive detectors typically require less signal processing circuitry than a digital output position sensor. However, developing a sensor with a direct readout from the sensor itself eliminates the need for any external output signal processing circuitry, which makes use of the device for various applications easier and less expensive. Consideration of these factors led to the development of the self-balancing position sensitive detector of the present invention.